The invention relates generally to video display systems and, more particularly, to systems for the display of electronically-generated data or images and television video.
Electrically operated and controlled displays are used for a wide range of applications in forms requiring the display of color or monochromatic imagery received from broadcast or closed circuit television systems or from synthetic imagery and symbology sources such as computers or radar systems. For instance, to provide the crew in an aircraft cockpit with sensor, performance, and flight information, multipurpose displays are required which are capable of displaying imagery, symbology, and other data generated by radar, flight computer, navigation, and other aircraft systems on an individually selected basis, or in combination through video overlay techniques.
Another application of electrically operated displays is in color television. Under prior art, a cathode ray tube having a light-emitting screen is constructed and operated to produce three colors synchronized with an external source of color video. In one method, the tube is constructed using a system of three electron guns, each of which receives the color video signal corresponding to one of the colors to be produced. Colored dots on the screen are energized by an electron stream emitted from each electron gun to produce the color picture. This method results in a relatively low resolution, low brightness, and low color quality picture.
Field sequential color display systems are an attempt to overcome the above limitations. These systems operate on the basis that the color picture is broken up into three pictures transmitted sequentially and displayed in superimposed fashion. Each picture is made up of one of the three primary color components (red, green or blue). By overlaying the picture components at a sufficiently rapid rate, the images appear to the eye to fuse into a composite full-color image.
Such field sequential color systems may include a set of color filters placed in front of a monochrome display monitor. The system is properly synchronized so that each picture color component is displayed with the color filter set to transmit the desired color. Unfortunately, field sequential color television is basically incompatible with existing color video transmission standards because the three pictures have to be transmitted in the time formerly used by one, with resultant three times increase in signal band width (if the same resolution is to be maintained). If one color frame is transmitted in each time frame, then the three colors are transmitted too slowly for the eye to combine them effectively, resulting in a flickering effect.
Attempts to solve these problems include the use of a multiple beam cathode ray tube to write a television type raster field, or frame, with the maximum data rate and writing speed reduced by a factor equal to the number of simultaneously-operating beams. The multiple beams sweep across the face of the cathode ray tube in paintbrush fashion, drawing two or more lines with each sweep. The frames are generated by vertically deflecting the plurality of beam sweeps down the screen with time so that each successive sweep paints the area directly below the previous sweep.
Conventional vertical deflection techniques utilize a constantly increasing deflection voltage. When applied to multiple beam cathode ray tubes, however, the vertical deflection must proceed at a greater rate to accommodate the added vertical distance which the beams must travel for each successive sweep. This results in a severely sloped picture requiring sophisticated electronics and complex calculations using polar coordinates in order to rotate the picture so that it may be accurately placed on the screen.